1. Field of the Invention
This invention relates to a stacked ceramic body, including ceramic layers and internal electrode layers that are alternately stacked with one another, that can be utilized as a piezoelectric device or a stacked ceramic capacitor.
2. Description of the Related Art
A stacked ceramic body produced by alternately stacking ceramic layers, containing a piezoelectric material and a dielectric material, and internal electrode layers, containing an electrode material, with one another can be widely utilized as a piezoelectric device and a stacked ceramic capacitor.
FIG. 19 of the accompanying drawings shows an example of a known stacked ceramic body. Ceramic layers 91 and 93 and internal electrode layers 92 and 94 are alternately stacked with one another as shown in the drawing. In this stacked ceramic body 9, right and left end faces 920 and 940 of the internal electrode layers 92 and 94 are respectively exposed on the right and left side surfaces 901 and 902. Dummy layers 99 are respectively stacked on the upper and lower ends in the stacking direction.
The stacked ceramic body 9 includes a right side surface electrode 941 electrically connected to the internal electrode layer 92 exposed on the right side surface 901, and a lead wire 95 connected to the right side surface electrode 941 through an electrically conductive paste 950. The stacked ceramic body 9 includes also a left side surface electrode 942 electrically connected to the internal electrode layer 94 exposed on the left side surface 902, and a lead wire 94 connected to the left side surface electrode 902 through the conductive paste 950. When the lead wires 95 are connected to an external power source (not shown in the drawing), voltages are applied to each ceramic layer 91, 93.
The stacked ceramic body 9 described above is produced in the following way.
A print portion for the internal electrode layer is printed on a green sheet for the ceramic layer either rightward (having a right end portion exposed on the right side surface after stacking) or leftward (having a left end portion exposed on the left side surface after stacking). A predetermined number of green sheets are stacked to give an unsintered stacked body.
The unsintered stacked body is introduced into a press-bond jig and is heated at 80xc2x0 C. to mutually press-bond the green sheet for the ceramic layer and the print portion for the internal electrode layer. Thereafter, degreasing, sintering, machining into a predetermined size, fitting of side surface electrodes, insulation, and so forth, are carried out to give the stacked ceramic body 9 shown in FIG. 19.
In a multi-stacked ceramic body having as many as hundreds of stacked layers, however, a difference of thickness reaching several millimeters occurs in some cases between each Y portion at which ceramic layers 91 and 93 are adjacent to each other in the stacking direction and an X portion at which the ceramic layers 91 and 93 are adjacent to each other through the internal electrode layers 92 and 94 as shown in FIG. 19.
Assuming that the number of the ceramic layers 91 and 93 is 500 and the thickness of the internal electrode layers 92 and 94 are 5 xcexcm, the difference of the thickness between the X portion and the Y portion is as great as 2.5 mm.
The difference of the thickness between the X portion and the Y portion has been absorbed in the past by inter-layer press-bonding of the green sheet and the print portion at the time of the unsintered stacked body. However, when the number of ceramic layers is as great as several hundred, inter-layer press-bonding cannot sufficiently absorb the difference.
In the stacked ceramic body sintered while inter-layer adhesion of the green sheet and the print portion is not sufficient, de-lamination (inter-layer peeling) is likely to develop.
Particularly in the case of a thin, stacked ceramic body having hundreds of thin ceramic layers stacked on one another, vigorous de-lamination such as cleavage of the ceramic layers from the side surface of the stacked ceramic body occurs.
It may be possible to employ a method that elevates the pressure in the press-bonding operation of the unsintered stacked body to prevent de-lamination, but the green sheet is likely to be broken. When the unsintered stacked body containing the damaged green sheet is sintered, cracks may develop inside the stacked ceramic body.
In view of the problems with the prior art technologies, this invention aims at providing a stacked ceramic body in which de-lamination (inter-layer peeling) does not easily occur, and a production method thereof.
According to a first aspect of the invention, there is provided a stacked ceramic body comprising a predetermined number of unit layers, each of the unit layers including a ceramic layer, an internal electrode layer stacked on at least a part of a surface of the ceramic layer, a spacer stacked on a surface of the ceramic layer at which the internal electrode layer is not formed, and having substantially the same thickness as the internal electrode layer, and adhesive layers stacked on a surface of the internal electrode layer and on a surface of the spacer.
Next, the operation and effect of the invention will be explained.
In the stacked ceramic body according to the first invention, the internal electrode layer and the spacer each having substantially the same thickness are stacked on the ceramic layer, and the adhesive layers are stacked on both the internal electrode layers and the spacers. Other ceramic layers are then stacked through the adhesive layers.
Therefore, the stacked ceramic body has a uniform thickness as a whole, and a partial difference of thickness does not easily occur. The adhesive layer ensures bonding between the ceramic layers. The adhesive layer can also absorb the difference of thickness between the internal electrode layer and the spacer.
The first invention described above can provide a stacked ceramic body in which de-lamination (inter-layer peeling) does not easily occur.
According to a second aspect of the invention, there is provided a method for producing a stacked ceramic body by stacking a predetermined number of unit layers, each of the unit layers including a ceramic layer, an internal electrode layer stacked on at least a part of a surface of the ceramic layer, a spacer stacked on a surface of the ceramic layer at which the internal electrode layer is not formed, and having substantially the same thickness as the internal electrode layer, and adhesive layers stacked on a surface of the internal electrode layer and on a surface of the spacer, the method comprising the steps of preparing slurry for a ceramic layer, containing a ceramic material and a binder, slurry for an internal electrode layer, containing an electrode material and a binder, slurry for a spacer, containing a spacer material and a binder, and slurry for an adhesive layer, containing an adhesive layer material and a binder; a binder content in the slurry for the adhesive layer being higher than a binder content in the slurry for the ceramic layer; forming a green sheet for a ceramic layer from the slurry for the ceramic layer; forming a print portion for the internal electrode layer on the green sheet for the ceramic layer by use of the slurry for the internal electrode layer; forming a print portion for the spacer by use of the slurry for the spacer; forming and stacking a print portion for the adhesive layer on the print portions for the internal electrode layer and for the spacer by use of the slurry for the adhesive layer to give an unsintered unit; stacking a predetermined number of the unsintered units to give an unsintered stacked body; and pressing and bonding the unsintered stacked body and then sintering the unsintered stacked body.
According to a third aspect of the invention, there is provided a method for producing a stacked ceramic body by stacking a predetermined number of unit layers, each of the unit layers including a ceramic layer, an internal electrode layer stacked on at least a part of a surface of the ceramic layer, a spacer stacked on a surface of the ceramic layer at which the internal electrode layer is not formed, and having substantially the same thickness as the internal electrode layer, and adhesive layers stacked on a surface of the internal electrode layer and on a surface of the spacer, the method comprising the steps of: preparing slurry for a ceramic layer, containing a ceramic material and a binder, slurry for an internal electrode layer, containing an electrode material and a binder, slurry for a spacer, containing a spacer material and a binder, and slurry for an adhesive layer, containing an adhesive layer material and a binder; a binder content in the slurry for the adhesive layer being higher than a binder content in the slurry for the ceramic layer; forming a large-scale green sheet capable of providing a plurality of green sheets for the ceramic layer from the slurry for the ceramic layer; forming a print portion for the internal electrode layer on the large-scale green sheet by use of the slurry for the internal electrode layer; forming a print portion for the spacer on the large-scale green sheet by use of the slurry for the spacer; forming and stacking a print portion for the adhesive layer on the print portions for the internal electrode layer and for the spacer by use of the slurry for the adhesive layer; punching the large-scale green sheet to give unsintered units; stacking and press-bonding the unsintered unit to other unsintered unit simultaneously with punching; repeating the formation, punching and press-bonding operations to give an unsintered stacked body; and sintering the unsintered stacked body.
Next, the operation and effect of the invention will be explained.
In the second invention, the unsintered stacked body is produced from the unsintered units each including the print portions for the internal electrode layer, for the spacer and for the adhesive layer that are formed on the green sheet. The unsintered stacked body is press-bonded and is then sintered.
In the third invention, each print portion is first formed on the large-scale green sheet and is then punched out to give the unsintered unit. The unsintered stacked boy is produced from the unsintered units and is then sintered. In this invention, the stacking and press-bonding operations of the unsintered units are carried out simultaneously with the punching-out operation.
In the production method according to the second and third inventions, the print portion for the internal electrode layer and the print portion for the spacer are formed on the green sheet as the ceramic layer, and the print portions for the adhesive layer are stacked on both of them. The binder content in the slurry for the adhesive layer is higher than the binder content in the slurry for the ceramic layer. Therefore, the green sheet as the ceramic layer can be firmly bonded to the print portion for the internal electrode layer and to the print portion for the spacer. The print portion for the adhesive layer can absorb the difference of thickness between the print portion for the internal electrode layer and the print portion for the spacer.
Therefore, in the stacked ceramic body obtained by the second and third production methods, the stacked ceramic body has a uniform thickness as a whole, and a partial difference of thickness does not easily occur. The adhesive layer strongly bonds the ceramic layers.
Because the slurry for the adhesive layer secures the bonding strength, it is not necessary to increase the bonding strength of the green sheet itself as the ceramic layer by increasing the binder amount of the slurry for the ceramic layer. In other words, the binder amount can be decreased. Furthermore, because sufficient degreasing need not be conducted by lowering the temperature rise rate during degreasing before sintering of the unsintered stacked body or degreasing at the time of sintering, the degreasing time and the sintering time can be shortened.
The third invention can particularly improve production efficiency because the press-bonding operation is carried out simultaneously with punching-out of the unsintered units.
The second and third inventions can provide a method for producing a stacked ceramic body in which delamination (inter-layer peeling) does not easily occur.